The present invention relates to the field of ink-jet printers.
With the advent of computers came the need for devices which could produce the results of computer generated work product in a printed form. Early devices used for this purpose were simple modifications of the then current electric typewriter technology. But these devices could not produce graphics or multicolored images, nor could they print as rapidly as was desired.
Numerous advances have been made in the field. The impact dot matrix printer is still widely used, but is not as fast or as durable as required in many applications, and cannot easily produce high definition color printouts. The development of the thermal ink-jet printer has solved many of these problems. Commonly assigned U.S. Pat. No. 4,728,963, issued to S. O. Rasmussen et al., describes an example of this type of printer technology.
Thermal ink-jet printers employ a plurality of resistor elements to expel droplets of ink through an associated plurality of nozzles. In particular, each resistor element, which is typically a pad of resistive material about 50 .mu.m by 50 .mu.m in size, is located in a chamber filled with ink supplied from an ink reservoir comprising an ink-jet cartridge. A nozzle plate, comprising a plurality of nozzles, or openings, with each nozzle associated with a resistor element, defines a part of the chamber. Upon the energizing of a particular resistor element, a droplet of ink is expelled by droplet vaporization through the nozzle toward the print medium, whether paper, fabric, or the like. The firing of ink droplets is typically under the control of a microprocessor, the signals of which are conveyed by electrical traces to the resistor elements.
The ink cartridge containing the nozzles is moved repeatedly across the width of the medium to be printed upon. At each of a designated number of increments of this movement across the medium, each of the nozzles is caused either to eject ink or to refrain from ejecting ink according to the program output of the controlling microprocessor. Each completed movement across the medium can print a swath approximately as wide as the number of nozzles arranged in a column on the ink cartridge multiplied times the distance between nozzle centers. After each such completed movement or swath, the medium is moved forward the width of the swath, and the ink cartridge begins the next swath. By proper selection and timing of the signals, the desired print is obtained on the medium.
The present invention is directed to the problem of controlling errors in the medium drive system due to gear backlash. The medium drive system typically includes a motor drive element, typically a stepper motor, which is connected to a drive motor through a gear train. Because it is essential for high print quality that the movement of the print medium through the print area be precisely controlled, backlash in the drive system can introduce serious accuracy errors.
This invention provides a solution to the problem of backlash in a printer medium drive system.